Hello, I hope the following is of help to you.
This will be due to a slight clutch drag caused by either a weak clutch cover or the clutch plate sticking on the transmission input shaft.
First put the car in gear and keep the clutch pressed, there should be no creep after any amount of time, if there is then this may point to a hydraulic concern although as you've checked the level this is unlikely.
Unfortunately to replace the clutch or even lubricate the input shaft splines means gearbox removal.
The reason that 1st and reverse are difficult is that the transmission is spinning all the time with the engine running, when you press the clutch certain components should stop spinning, as the clutch plate isn't completely disengaging these transmission components are still spinning, when you try to engage a gear you need to overcome this clutch drag. Once in gear the transmission will have stopped spinning which is why with the clutch still pressed you can engage the gears easier, if you release the clutch and try again you will find the gears difficult again.
The other gears are OK when driving as the drag isn't sufficient to affect the transmission while in motion, this is why there is no crunching either.
I hope this is clear enough and answers your question.